<script>

// returns the current hour
function GetCurrentHour()
{
  // obtain the current hour
  var date = new Date();
  var hour = date.getHours();
  // return the hour
  return hour;
}

// display greeting
function DisplayGreeting(hourFunc)
{
  // retrieve the hour using the function received as parameter
  hour = hourFunc();
  // display greeting
  if (hour >= 22 || hour <= 5)
    document.write("Goodnight, world!");
  else
    document.write("Hello, world!");
}

// call DisplayGreeting
DisplayGreeting(GetCurrentHour);

</script>